Such a hydraulic system is described, for example, in DE 10 2008 038 793 A1. The vehicle for which the known system is intended is an excavator having two crawlers, each crawler being driven by one of the two hydraulic circuits. Furthermore, each hydraulic circuit can be used to operate a further hydraulic consumer, like a turning drive for the upper part of the excavator, for the bucket, etc.
Under normal circumstances the two hydraulic circuits are connected to each other. The connecting means can interrupt this connection when the demand of hydraulic flow in one circuit is smaller than the maximum capacity of the respective pressure source and larger than a switching demand is. Such a switching demand can be, for example, 80% of the maximum capacity of the respective pressure source.
An excavator usually has rather constant operational conditions. As a rule it repeats a sequence of movements for a number of times.
Other vehicles show other behaviors. A tractor, for example, has to be driven on a road and in a field. Driving on the road requires a higher velocity than driving in a field. Furthermore, the steering behavior of a tractor on the road is different from the behavior in the field. During operation in a field, hydraulic consumers have to be actuated, for example a hitch or a front loader.
The use of different hydraulic circuits each being provided with an own pressure source has advantages in view of energy consumption and efficiency. However, in order to fulfill safety requirement control of the flow between the circuits can be complicated and cumbersome.